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ISL6327 Datasheet, PDF (12/30 Pages) Intersil Corporation – Enhanced 6-Phase PWM Controller with 8-Bit VID Code and Differential Inductor DCR or Resistor Current Sensing
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ISL6327
VIN
ISL6609
PWM(n)
IL(s)
L
DCR
INDUCTOR
VL
VC(s)
R
C
VOUT
COUT
ISL6327 INTERNAL CIRCUIT
In
RISEN(n)
(PTC)
CURRENT
SENSE
ISEN-(n)
+
-
ISEN+(n)
CT
ISEN
=
IL
---D----C-----R-----
RISEN
FIGURE 3. DCR SENSING CONFIGURATION
If the R-C network components are selected such that the
RC time constant (= R*C) matches the inductor time
constant (= L/DCR), the voltage across the capacitor VC is
equal to the voltage drop across the DCR, i.e., proportional
to the channel current.
With the internal low-offset current amplifier, the capacitor
voltage VC is replicated across the sense resistor RISEN.
Therefore the current out of ISEN+ pin, ISEN, is proportional
to the inductor current.
Because of the internal filter at ISEN- pin, one capacitor CT
is needed to match the time delay between the ISEN- and
ISEN+ signals. Select the proper CT to keep the time
constant of RISEN and CT (RISEN x CT) close to 27ns.
Equation 6 shows that the ratio of the channel current to the
sensed current ISEN is driven by the value of the sense
resistor and the DCR of the inductor.
ISEN
=
IL
⋅
---D----C-----R-----
RISEN
(EQ. 6)
RESISTIVE SENSING
For accurate current sense, a dedicated current-sense
resistor RSENSE in series with each output inductor can
serve as the current sense element (see Figure 4). This
technique is more accurate, but reduces overall converter
efficiency due to the additional power loss on the current
sense element RSENSE.
The same capacitor CT is needed to match the time delay
between ISEN- and ISEN+ signals. Select the proper CT to
keep the time constant of RISEN and CT (RISEN x CT) close
to 27ns.
Equation 7 shows the ratio of the channel current to the
sensed current ISEN.
ISEN
=
IL
⋅
R-----S----E----N----S----E--
RISEN
(EQ. 7)
IL
L
RSENSE VOUT
COUT
ISL6327 INTERNAL CIRCUIT
In
RISEN(n)
CURRENT
SENSE
ISEN-(n)
+
-
ISEN+(n)
CT
ISEN
=
IL
-R----S----E-----N-----S----E---
RISEN
FIGURE 4. SENSE RESISTOR IN SERIES WITH INDUCTORS
The inductor DCR value will increase as the temperature
increases. Therefore the sensed current will increase as the
temperature of the current sense element increases. In order
to compensate the temperature effect on the sensed current
signal, a Positive Temperature Coefficient (PTC) resistor can
be selected for the sense resistor RISEN, or the integrated
temperature compensation function of ISL6327 should be
utilized. The integrated temperature compensation function
is described in the Temperature Compensation section.
Channel-Current Balance
The sensed current In from each active channel are summed
together and divided by the number of active channels. The
resulting average current IAVG provides a measure of the
total load current. Channel current balance is achieved by
comparing the sensed current of each channel to the
average current to make an appropriate adjustment to the
PWM duty cycle of each channel with Intersil’s patented
current-balance method.
Channel current balance is essential in achieving the
thermal advantage of multiphase operation. With good
current balance, the power loss is equally dissipated over
multiple devices and a greater area.
12
FN9276.2
December 20, 2006
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